Field of the Invention
The present invention relates to a control apparatus for controlling a controlled object having a response lag characteristic, including an internal combustion engine and an accessory device thereof.
Description of the Related Art
Conventionally, as a control apparatus, one disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2005-171893 is known. This control apparatus controls boost pressure by controlling a variable nozzle type turbocharger as a controlled object. This control apparatus calculates a target boost pressure epimtrg according to operating conditions of the engine, and feedback-controls an actual boost pressure epim such that the actual boost pressure epim becomes equal to the target boost pressure epimtrg, using a feedback control algorithm including an integral term.
With this feedback control algorithm, a boost pressure difference epimdlt, which is a difference between the actual boost pressure epim and the target boost pressure epimtrg, is calculated, and a feedback control term epvnpmfb is calculated based on the boost pressure difference epimdlt, as a total sum of a proportional term epvnpmp, an integral term epvnpmi, and a derivative term epvnpmd, by a PID control method. Further, a sum epbnbse+epvnpmfb of the feedback control term epvnpmfb and a basic value epbnbse of boost pressure is compared with a predetermined minimum limiting value epvnpmin, and then the larger one of them is compared with a predetermined maximum limiting value epvnpmax, whereby the larger one of them is set as a final opening epvnfin. Then, the actual boost pressure epim is feedback-controlled such that the actual boost pressure epim becomes equal to the target boost pressure epimtrg by controlling supply current to a DC motor according to the final opening epvnfin.
In calculation of the integral term epvnpmi, when predetermined update inhibiting conditions are satisfied in a transient operating condition of the engine, an update of the integral term epvnpmi is inhibited, and the integral term epvnpmi is maintained at the immediately preceding value thereof. This is for avoiding an overshoot of the actual boost pressure epim, because, in the case of the variable nozzle type turbocharger, the actual boost pressure epim has a characteristic of being liable to overshoot with respect to the target boost pressure epimtrg due to a response lag, and this problem becomes more conspicuous in a transient operating condition of the engine.
In the above conventional control apparatus, when the predetermined update inhibiting conditions are satisfied, the update of the integral term epvnpmi is inhibited, however, if it is determined that the predetermined update inhibiting conditions are not satisfied in a state where the actual boost pressure epim is below the target boost pressure epimtrg, the update of the integral term is started from the time of the determination. In this case, the integral term is increased after the start of the update of the integral term, which may result in overshoot of the actual boost pressure epim with respect to the target boost pressure epimtrg.
To avoid this inconvenience, if the update inhibition period of the integral term is set longer, after starting the update of the integral term, the actual boost pressure epim may not reach the target boost pressure epimtrg, or to the contrary, there may occur an excessive overshoot due to causing the actual boost pressure epim to be rapidly made closer to the target boost pressure epimtrg. The above problems become more conspicuous in a case where the variable nozzle type turbocharger suffers from variation in characteristics between individual products thereof or aging, and also become conspicuous under a condition that a sudden increase/decrease in the demand of output from the engine by a driver is repeated.